The present invention relates to fiber reinforced plastic wheels (commonly known as FRP wheels) for passenger and commercial transportation motor vehicles. More particularly, the invention relates to a means and method for attaching such FRP wheels to the mounting plates on such vehicles.
An FRP wheel is a known type of wheel for motor vehicles, and is formed by molding a one-piece wheel out of fiber reinforced plastic. The RFP wheel is in turn attached to the motor vehicle mounting plate by a plurality of attachment studs, each of which passes through the mounting plate and a hole through the wheel disc, and a plurality of mounting nuts, each of which is torqued on to the end of an attachment stud. In a common method of production of an FRP wheel, the wheel is initially molded with no holes for the attachment studs, the holes thereafter being drilled or machined into the wheel disc.
One of the difficulties with the preceding method of construction and attachment is that the drilling of the wheel disc holes causes reinforcing plastic fibers in the disc to be severed and exposed at the internal circumferential surfaces of the holes defining the holes passing through the discs. These exposed and severed fibers allow for intrusion of environmental liquids and vapors along the fiber/resin interfaces surrounding the holes, which in turn causes degradation of the FRP wheels in the internal areas adjacent to the holes. A further difficulty associated with this method of construction and attachment is that the severed and exposed fibers surrounding the holes increase the sliding friction between cone seating mounting nuts and the frustoconical hole surfaces laterally adjacent where frustoconical portions of the mounting nuts extend into the holes upon tightening. The sliding friction also may increase between the hole surfaces and the attachment studs passing through the holes. As is known, such increases in sliding friction result in lower clamping forces holding the wheel onto the mounting plate, particularly at high temperatures.
Various methods have been attempted to either protect the hole surfaces and/or provide acceptable clamping forces to hold the wheel onto the mounting plate, both results of course being highly desirable to obtain a safe, long lasting and properly functioning wheel mounting. Such prior art methods have variously included at least the following: (1) molding or fitting metal or plastic or FRP inserts or sleeves into the disc to provide the surfaces surrounding the mounting holes; (2) attempting to control the distribution and orientation of reinforcing fibers, particularly in the areas adjacent where the holes are drilled into the wheel; (3) casting the wheel holes directly into the wheel during the molding of the FRP wheel, including the use of an FRP composition that is highly resistant to creep; and (4) applying an antiseize lubricant paste onto the frustoconical hole seating surfaces for the cone seating nuts prior to assembly of the nuts. The first method is costly, and in some instances may cause casting problems and cracking in the wheel. The second method does not solve the above-noted problems associated with severed and exposed fibers at the surfaces surrounding the bolt holes. The third method results in uneven distribution and orientation of the reinforcing fibers adjacent the holes during casting of the wheels, and cracking in unreinforced areas. The fourth method presumable results in a decrease in sliding friction and may partially (i.e., at the frustoconical seating surfaces) protect the exposed fibers from environmental exposure, but only temporarily since the antiseize lubricant is not mechanically or chemically attached and can be removed during application of the mounting nuts, maintenance and cleaning, exposure to the environment, and continued wear and abrasion from all surfaces that come into contact with the antiseize lubricant. Once the antiseize paste is removed, the fibers will again be exposed to the environment around the holes and further there will be no means present to reduce friction in the subsequent reattachments of the wheel to the mounting plate.
It will accordingly be seen that the mounting holes in FRP wheels have presented the above noted long-standing problems that to date have not been adequately solved.
Prior art representing the above prior methods may be found for example within U.S. Pat. Nos. 3,309,843; 3,811,737; 3,870,372; 4,294,490; 4,294,639; 4,489,184; 4,569,957; 5,022,712; 5,123,711; 5,234,259; 5,277,479; 5,401,079; and Japanese Patent Application 02-128958.
The present invention is intended to overcome the deficiencies of the above-noted prior art. A vehicle wheel is disclosed wherein the holes in the wheel disc are drilled or machined after the one-piece wheel has been molded out of fiber reinforced plastic. The holes may include frustoconical seating surfaces for cone seating nuts, spherical seating surfaces for nuts with a spherical radius, or the holes may be cylindrical through the disc in which event flange nuts are used for mounting. Following the forming of the holes, which initially have severed and exposed fibers at the surfaces surrounding the holes, a thin and smooth protective coating of a thermoset resin is permanently created on all the internal surfaces surrounding the holes all the way from the outboard side of the disc to the mounting plate side of the disc. This is accomplished by first applying onto these surfaces a layer of a mixture of thermoset resin and curing and coupling agents. In the case of frustoconical and spherical seating surfaces, a molding plug matching the shape and final specified dimensions of each hole, from one disc side to the other, is inserted into each hole and positioned to mold the thermoset resin layer between the plug outer surface(s) and the circumferential surfaces(s) defining the hole to the final specified dimensions of the hole. The mold plug has a centering portion so that the plug mating surfaces are concentric with the hold. As the plug is inserted, it pushes excess resin mixture out the other end of the hole and also into the interstices between the fibers and resin in the wheel adjacent the hole. A curing operation is then carried out to cure the thermoset resin to its final condition and dimensions(s). The resin mixture atomically and mechanically bonds with the exposed and severed hole fibers and the wheel resin adjacent the hole. The mold plug is then removed. The exposed fibers surrounding each hole from one disc side to the other accordingly are covered by a permanent protective, thin and smooth, layer of cured thermoset resin. The fibers surrounding each hole accordingly are not subject to environmental liquids and vapors, and thus there is no intrusion along fiber interfaces anywhere along the hole to degrade the wheel adjacent the holes. In the case of a fully cylindrical hole through the disc, the mold plug may not be needed.
The method of the present invention results in a permanent layer that is not removed during exposure to the environment, and that is strong enough so as not to be removed by continued wear and abrasion by the attachment nuts. Likewise, there will not be excessive sliding friction during reattachment of the wheels. Generally, the permanently cured layer will be thick enough to remain intact under the aforementioned environmental, wear and abrasion influences, but thin enough not to cause degradation in long-term clamping force from creep. A thickness of 0.001 inches, for example, is thought to be appropriate to meet these criteria. The resin should be selected to cure to a smooth (i.e., low coefficient of friction) condition, allow removal of the hole plug after curing, and be compatible with the wheel FRP material adjacent to the holes.
The present invention is also applicable to dual wheels mounted to the same mounting plate wherein the attachment studs pass from the mounting plate through the discs of each of the dual wheels before the mounting nuts are attached. Furthermore the same method may be used to form permanent coatings on other holes having exposed and severed fibers in the FRP disc or rim, for example valve holes, center hub holes or other holes drilled or machined into the disc face to reduce weight, add styling features or serve some other design purpose.
Other features and advantages of the present invention will be apparent from the following description, drawings and claims.